Conversion and coking of hydrocarbon oils



5p w .W w mg flwwi mu m 4 W 2 5 n 0 H 0 M m a 2 e 4 lw I 4 w ma Original Filed. Aug. 21, 193-5 Ea cll'argazor L C HUFF CONVERSION AND COKING OF HYDROCARBON OILS Patented Apr. 19, 1938 UNITED s-T'rs PATET FliTLE CONVERSION AND COKING OF HYDRO- CARBON OILS ration of Delaware Application August 21, 1933, Serial No. 686,110 Renewed September 11, 1937 5. Claims.

This invention particularly refers to improve-- ments in the type of process and apparatus wherein hydrocarbon oil is subjected to pyrolytic conversion for the production, primarily, of low boiling distillate, comprising materials within the boiling range of gasoline, and petroleum coke, said improvements comprising a method and means for substantially devolatilizing the coke so produced within the same system wherein it is produced and without extensive additional equipment.

Cracking processes of the type wherein hydrocarbon oil is subjected to conversion temperature at substantial superatmospheric pressure in a heating coil, the heated oil introduced into a reaction chamber also maintained at superatmospheric pressure, wherein it is subjected to continued conversion without additional heating and the residual conversion products are reduced to coke, and the resulting vaporous conversion products subjected to fractionation. for the recovery of a light distillate product, such as motor fuel, or, more commonly, a product termed pressure distillate, the major component of which is material within the boiling range of gasoline, are now well known and extensively used. The coke produced in such a process varies considerably, depending upon the type of charging stock and the operating conditions employed and the character of the coke deposited at different points in the reaction chamber during a single operating cycle may vary considerably, the volatility ranging, in some cases, from 2-6% in the lower portion of the chamber to as much as 10-20% in the upper portion of the chamber.

The present invention is concerned with improvements to the type of operation above described by means of which the coke deposited in the reaction chamber at the end of the normal operating cycle of the process is subjected to devolatilization whereby to produce a more valuable and a more readily marketablelcoke and whereby a coke deposit of substantially uniform volatility and physical structure is obtained throughout the mass of coke deposited in the reaction chamber. This is accomplished by circulating through the heating coil, after the normal cracking cycle is completed and the chamber is substantially filled with coke, low boiling hydrocarbon oil distillate, comprising the distillate produced by said cracking operation or similar oil from an external source, and passing the highly heated distillate into direct contact with the mass of coke accumulated in the reaction chamber to impart additional heat thereto and thereby vaporize a substantial proportion of its volatile components.

As an alternative to the devolatilizing step above described or as a subsequent step to effect further devolatilization of the coke, steam may 5 be passed through the heating coil and subjected therein to superheating and superheated steam introduced into the reaction chamber in direct contact with the bed of coke imparting additional heat thereto and efiecting its further devolatil- 10 ization. This provision is particularly desirable in case carbonaceous material is deposited in the heating coil, as the steam will tend to loosen and assist removal of such carbonaceous deposits and, when desired, a temperature of the order of 1700 l to 2000 F., or thereabouts, may be employed in the heating coil during a portion or all of this stage of the process in order to induce a watergas reaction between the coke and the highly superheated steam. 0

One specific embodiment of the present invention may comprise continuously passing hydrocarbon oil charging stock through a heating coil wherein it is subjected to a conversion temperature at substantial superatmospheric pressure and introducing the heated products into a reaction chamber also maintained at substantial superatmospheric pressure, wherein they are sub jected to continued conversion Without additional heating, the vaporous conversion products sepa- 30 rated from the non-vaporous residual conversion products and the latter reduced to coke therein, subjecting the vaporous conversion products to fractionation whereby their components boiling below the range of the desired light distillate 35 product of the process are condensed as reflux condensate, returning reflux condensate to the heating coil for further conversion, together with the charging stock, subjecting fractionated vapors of the desired end boiling point to condensa- 40 tion, recovering the resulting distillate, continuing this operation until the reaction chamber is substantially filled with coke, then stopping the supply of raw oil charging stock to the process but continuing the circulation of reflux conden- 45 sate through the heatingcoil into the lower portion of the reaction chamber, gradually replacing the reflux condensate supplied to the heating coil with said distillate recovered during the preceding operation of the process, heating the dis- 50 tillate therein to the desired temperature, equal to or in excess of the conversion temperature previously employed, and continuously passing the highly heated distillate upward through the bed of coke in the reaction chamber until the 55 the resulting distillate recovered while reflux condensate recovered by such fractionation is preferably withdrawn from the system.

Various modifications and alternatives to the specific embodiment above described which, however, are not to be considered equivalent, have been previously indicated and will be more apparent with reference to the following description of the accompanying diagrammatic drawing, which illustrates one specific form of apparatus embodying the features of the present invention and in which the process of the present invention may be accomplished.

Referring to the drawing, raw oil charging stock for the process is supplied through line I and valve 2 to pump 3 by means of which it is fed through line 4 andmay pass either through line 5 and valve 6 into fractionator I or, all or in part, through line 8, valve 9 and line In direct to heating coil I I. That portion, if any, of the charging stock supp-lied to fractionator i, as indicated, serves to assist fractionation of the vaporous conversion products in this zone by direct contact therewith and is thereby preheated, collecting together with the reflux condensate resulting from fractionation of the vapors in the lower portion of the fractionator to be withdrawn therefrom through line I2 and valve I3 to pump I4 by means of which the reflux condensate or reflux condensate and preheated raw oil, as the case may be, is supplied through line II and valve I5 to conversion in heating coil I I. It will be understood that the charging stock may, when desired, be preheated in any other well known manner (not shown) prior to its introduction into the heating coil.

Heating coil I I is located in a furnace I6 of any suitable form by means of which suflicient heat is imparted to the oil passing through this zone to bring it to the desired conversion temperature, preferably at a substantial superatmospheric pressure and the heated products are discharged through line H and valve 18 into reaction chamber I9.

Chamber I9, like heating coil II, is preferably maintained at a substantial superatmospheric pressure during the normal cracking operation and this zone is preferably well insulated against the excessive loss of heat by radiation so that conversion of the heated products supplied thereto from heating coil I I may continue therein. In the present process the extent of continued conversion accomplished in chamber I9 is suflicient to effect the reduction of the residual conversion product of the process to coke which is allowed to accumulate within chamber I9 until it is substantially filled. Chamber I9 is provided with a drain line 20, controlled by valve 2|, which may also serve as a means of introducing steam, water or any other suitable cooling medium into the bed of devolatilized coke within the chamber, after the devolatilizing stage of the process is completed, in order to hasten cooling and facilitate cleaning of the chamber in order to prepare it for subsequent operation.

Vaporous conversion products of the process pass from the upper portion of chamber I9 through line 22 and valve 23 to fractionation in fractionator I wherein their components boiling above the range of the desired overhead vaporous product are condensed as reflux condensate, to be returned during the normal cracking operation to further conversion in heating coil II, as already described.

Fractionated vapors of the desired end boiling point pass from the upper portion of fractionator I through line 24 and valve 25 to be subjected to condensation and cooling in condenser 26. The resulting distillate and gas passes through line 21 and valve 28 to collection and separation in receiver 29. Uncondensable gas may be released from the receiver through line 30 and valve 3|. The distillate may be withdrawn through line 32 and valve 33 to storage or to any desired further treatment or may pass from line 32 through line 36 and valve 35 to run-down tank 36. A regulated portion of the distillate collecting in receiver 29 may, when desired, be withdrawn therefrom through line 31 and valve 38 to pump 39 to be recirculated through line 40, valve M and line 42 and valve 58 to the upper portion of fractionator 'l to assist cooling and fractionation of the vapors in. this zone and to control the vapor outlet temperature from the fractionator, thus regulating the end boiling point of the overhead product from this zone.

When chamber I9 has been substantially filled with coke the usual practice in an operation such as above described is to shut down the process and clean the system preparatory to another similar operation, which shut-down is accomplished in any of several well known manners with which the present invention is not concerned. In the process of the present invention, however, although the normal cracking operation is halted at this point actual operation of the process is not terminated and the subsequent steps of the operation, to be presently described, comprise the novel features of the present invention.

In the present invention when chamber I9 has been filled with coke to the desired extent the supply of raw oil charging stock to the process is stopped but the circulation of reflux condensate from fractionator I through heating coil II into chamber I9 is continued. During this period the reflux condensate is heated in heating coil II, preferably to a temperature substantially the same or somewhat higher than the temperature previously employed in this zone during the normal cracking operation but the heated oil instead of entering the upper portion of chamber I9 through line I! and valve I8, as previously described and illustrated, is preferably introduced into the lower portion of chamber I9, for example, through line 43 and valve 44 so that the heated products from the heating coil pass upward through the mass of coke accumulated in chamber I9, serving the purpose of supplying ad ditional heat to the coke mass and serving as a vaporizing medium and/or solvent for any unvaporized oil or pitchy material remaining in the bed of coke at the end of the normal cracking operation. During this period of the operating cycle vaporous products pass from the coking chamber, as before, through line 22 and valve 23 to fractionation in fractionator I and distillate from receiver 29 or from tank 36, or both, is recirculated to fractionator I to serve as a cooling and refluxing medium, the same vapor outlet temperature from the fractionator as that employed during the normal cracking operation preferably being maintained and the overhead distillate product is collected in receiver 29 in the manner previously described. The return of distillate from tank 36 to fractionator I is accomplished by means of line 45, valve 46, pump 41, line 48, line 49, valve 50, line 42 and valve 58.

The period of the operating cycle just described serves to dispose of the reflux condensate remaining within the system at the end of the normal cracking operation and may be considered a conditioning step preceding the devolatilizing stage of the process. The reflux condensate will be converted into lower boiling and higher boiling products during this stage of the process and will become heavier as the operation progrosses. It will also diminish in quantity and will be gradually replaced by distillate from tank 36 or by similar material from any desired external source, the distillate preferably being supplied from pump 41 through line 48, valve 5| and line l direct to heating coil ll. When distillate from an external source is utilized for this purpose it may be supplied topump 41 through line 52 and valve 53. When desired, this conditioning stage, prior to actual devolatilization of the coke, may be dispensed with by supplying distillate from pump 36 or from an external source to heating coil H, in the manner already described, immediately after the normal cracking stage of the process; When this method of operation is employed as soon as the supply of raw oil charging stock to the process is stopped, reflux condensate from fractionator l is diverted through line 54 and valve 55 to cooling and storage or elsewhere, as desired.

The distillate supplied to heating coil H from tank 36 or from an external source, as already indicated, depending upon its characteristics and the desired results, as will be later more fully described, is heated therein to substantially the same or to an appreciably higher temperature than that employed in this zone during the previous stage of the process and the heated distillate is introduced preferably into the lower portion of chamber it, for example, through line 43 and valve 44, passing upward through the mass of coke in chamber 19 to further heat \and substantially devolatilizing the same. It will be understood that although only one point of introduction for the heated distillate to chamber i9 is shown in the drawing it may be introduced at any other desired point or at a plurality of points in this zone and it is within the scope of the present invention to introduce the heated distillate at progressively higher points in the chamber as devolatilization of the coke progresses whenever this procedure is necessary in order to obtain a coke deposit of substantially uniform volatility throughout the chamber. This may be accomplished, for example, by means of branch lines (not shown) from line H, similar to line 43 and valve 44, entering chamber I9 at any desired point.

During the devolatilizing step just described vaporous products from chamber I!) pass through line 22 and valve 23 to fractionation in fractionator I, as in the previous stages of the operation. The reflux condensate resulting from fractionation in fractionator 1 during this stage of the operation is preferably diverted from the system to cooling and storage or elsewhere, as desired, through line 54 and valve 55. During this period of the operating cycle fractionation of the vaporous products supplied to fractiona tor 7 may be controlled, preferably, by means of distillate recirculated, as previously described, from receiver 29 to the upper portion of the fractionator to accomplish the removal, as the overhead vaporous product from the fractionator, of materials boiling entirely within the range of the desired final motor fuel product of the process, thus in addition to serving as a heat carrying medium to effect devolatilization of the coke, a pressure distillate produced during the normal cracking operation may be redistilled to produce end-point motor fuel or may be reformed to produce a. motor fuel product of higher anti-knock value, by employing suitable conditions in heating coil E l, or, when the motor fuel components are of satisfactory anti-knock value, the conditions employed in heating coil I I may be regulated to secure conversion of substantially only the higher boiling fractions of the pressure distillate for the production of additional yields of good quality motor fuel. It is also, of course, within the scope of the present invention to produce an overhead product from fractionator 1 of end point motor fuel characteristics during the normal cracking operation and to subject this product to reforming in heating coil it during the subsequent devolatilizing stage of the process for the purpose of materially improving its anti-knock value without excessively altering its boiling range. The devolatilizing stage of the process may also be conducted, when desired, for the purpose of converting or reforming a light distillate such as straight-run gasoline, naphtha, kerosene, kerosene distillate, or the like, or mixtures of such materials from an external source or, when conversion or reforming of the light distillate employed as the heat carrying medium is not desired, the conditions employed in heating coil I! may be regulated to avoid such conversion and/or reforming.

The devolatilizing stage of the process above described may, when desired, be succeeded by a period of further devolatilization of the coke by means of superheated steam or the steam devolatilizing step may be utilized without the previous stage of devolatilizing with heated distillate. When steam is employed for this purpose it may be supplied to heating coil H from any suitable generating source, (not shown), through line 55, valve 5"? and line H], the steam being subjected to a high degree of superheat as it passes through heating coil M and the superheated steam is introduced into the bed of coke in chamber it, for example, through line 43 and valve 44 or at any other desired point, as previously described in connection with the introduction of heated distillate into this zone.

The method of devolatilizing the coke with superheated steam is particularly desirable in case a very low volatile coke is required and/or when any considerable deposit of carbonaceous material is. left in the heating coil during the previous cracking and/or devolatilizing stages, the superheated steam serving not only as a heat carrying medium to devolatilize the coke, but also serving, when desired, as a means of removing or assisting subsequent removal of the carbonaceous deposit in the heating coil. When desired, the temperature employed in heating coil ll during this stage of the process may be sufficient to induce a water-gas reaction between the superheated steam and the coke.

When devolatilization with superheated steam is employed the steam and the hydrocarbon vapors may pass from chamber l9 through line 22 and valve 23 into fractionator i which may serve as a contact condenser by introducing water, distillate or any other suitable cooling medium into this zone through line 5 and/or line 42 or at any other suitable point (not shownh s in which case the resulting water and distillate may be withdrawn from fractionator I through line 54 and valve 55 to separation by any well known means (not shown). It is also within the scope of the present invention, when this method of operation is employed, to utilize the heat contained within the steam and other products supplied to fractionator l to rerun the distillate produced in a previous stage of the process or, for example, to top crude oil or to fractionally distill any other desired material. Distillate produced in the previous stage of the operation may be supplied for the purpose mentioned to fractionator 1 from tank 36, in the manner previously described, or oil from another source may be supplied to this zone by means of pump 3 or pump Al, in the manner previously described. When fractionator l is thus used as a re-running or topping column or the like the desired overhead distillate product may be collected and separated from any water, resulting from the condensation of steam collected therewith, in receiver 29 and the bottoms may be withdrawn from the lower portion of the fractionator and removed from the system through line 54 and valve 55.

During the normal cracking operation, Where in coke is deposited in the reaction chamber for subsequent devolatilization, the operating conditions may be approximately as follows: The conversion temperature employed at the outlet from the heating coil H is preferably Within the range of 900 to 950 F. with a superatmospheric pressure at this point in. the system ranging, for example, from 100 to 500 pounds, or thereabouts per square inch. Substantially the same pressure as that employed at the outlet from heating coil is preferred in the reaction chamber, although somewhat reduced superatmospheric pressure may be employed in this zone, when desired. The pressure employed in the fractionating, condensing and collecting portions of the system may be substantially equalized with or somewhat reduced relative to the pressure employed in the reaction chamber.

The temperature to which the distillate is heated in the heating coil during the devolatilizing stage of the process is preferably at least as high as the temperature to which the hydrocarbon oil is heated in this zone during the normal cracking operation. This temperature is usually within the range of 90-0 to 950 F., or thereabouts. When the distillate utilized as the heat carrying medium for devolatilization of the coke comprises or contains a substantial proportion of materials within the boiling range of motor fuel but of poor anti-knock value, the conditions to which the distillate is subjected in the heating coil may be sufiiciently severe to accomplish reforming of the motor fuel fractions to materially improve their anti-knock value without excessively altering their boiling range, the temperature in such cases ranging, for example, from 950 to 1050 F. and when this type of operation is employed the pressure employed at the outlet from the heating coil is preferably in excess of 350 pounds, or thereabouts, per square inch, the preferred range being from 500 to 1000 pounds per square inch, or thereabouts. When conversion of the high boiling fractions of the distillate is desired, to produce substantial yields of good quality motor fuel without any extensive reforming of its lower boiling fractions, the conditions employed at the outlet from the heating coil are preferably within the range of 900 to 960 F., or thereabouts, with a superatmospheric pressure of the order of 100 to 500 pounds per square inch. When such conversion and/or re forming of the distillate employed as the heat carrying medium for the devolatilizing operation is not desired lower pressures are ordinarily preferred in the heating coil ranging, for example, from substantially atmospheric to 100 pounds, or thereabouts, per square inch, in which case the temperature, depending upon the character of the distillate employed as the heat carrying medium and upon the desired degree of devolatilization, may range, for example, from 900 to 1000 F., or thereabouts.

The pressure employed in the reaction chamber during devolatilization of the coke with heated distillate is preferably of a low order ranging, for example, from substantially atmospheric to 100 pounds, or thereabouts, per square inch, although higher pressures up to 500 pounds, or more, per square inch may be employed, when desired, particularly in case substantial conversion or reforming of the distillate employed as the heat carrying medium is desired.

When superheated steam is employed as the heat carrying medium-to devolatilize the coke the temperature at the outlet from the heating coil may range, for example, from 1000 to 2000 F., or thereabouts. Preferably, in such operations substantially atmospheric or low superatmospheric pressure is employed in the reaction chamber. Preferably, substantially atmospheric or low superatmospheric pressure is also employed in the heating coil, although a superatmospheric pressure up to 500 pounds per square inch, or thereabouts, may be employed in this zone, when desired, in which case a lower outlet temperature than that above mentioned may be successfully employed.

As a specific example of one of the many possible operations of the process of the present invention utilizing a 23 A. P. I. gravity Mid-Continent fuel oil as charging stock; this material is subjected together with reflux condensate from the fractionator to a conversion temperature of approximately 900 F. at the outlet from the heating coil, a superatmospheric pressure of approximately 250 pounds per square inch is employed at this point in the system and is substantially equalized in the reaction chamber and succeeding fractionating, condensing and collecting equipment. Coke is allowed to accumulate in the reaction chamber and when it has become substantially filled the supply of raw oil charging stock to the heating coil is stopped but the flow of reflux condensate from the fractionator to the heating coil is continued, pressure distillate from the receiver of the system being supplied to the fractionator as refluxing material. During this period of the operation the temperature at the outlet from the heating coil is raised to approximately 925 F. Distillate from the previous stage of the operation is supplied to the fractionator and the reflux condensate is gradually replaced with pressure distillate bottoms resulting from redistillation of the pressure distillate supplied to the fractionator. The temperature at the outlet from the heating coil is increased during this stage of the operation to approximately 1000 F. with a superatmospheric the distillate recovered during the first stage of the operation is redistilled and the resulting pressure distillate bottoms subjected to further conversion. A motor fuel of about 385 F. endboiling point is recovered during this stage of the operation.

An operation such as described may yield, per barrel of charging stock, during the first stage of the operation, about 60 percent of pressure distillate containing approximately percent of 400 end-boiling point motor fuel having an octane number of approximately 65, about pounds of coke and about 700 cubic feet of rich uncondensable gas. During the pressure distillate redistilling operation wherein the pressure distillate bottoms are subjected to further conversion in the heating coil and the heated products utilized to devolatilize the coke, the antiknock value of the motor fuel is increased to an octane number of approximately 70 and the average volatility of the coke is decreased from approximately 10 percent to less than 5 percent. The final yield of motor fuel based on the fuel oil charging stock may amount to approximately 53 percent. The weight of coke produced is somewhat decreased during the devolatilizing stage and a considerable quantity of additional gas is produced.

It will be understood that the above example is descriptive of only one of the many possible types of operations which may be practiced Within the scope of the present invention and it is not intended to limit the invention to the details of the operation above given nor to the particular operating conditions and results shown.

I claim as my invention:

1. In the coking of hydrocarbon oils wherein heavy hydrocarbon oil is heated in a coil and subsequently distilled to coke in an enlarged chamber and passage of the oil through the heating coil continued until a substantial body of coke has accumulated in the chamber, the evolved vapors fractionated and resultant reflux condensate returned to the coil for retreatment with the heavy oil; the method which comprises discontinuing the supply of the heavy oil to the coil when a substantial body of coke has accumulated in the chamber, continuing the return of reflux condensate to the heating coil, introducing the heated reflux condensate into direct contact with the mass of coke accumulated in the chamber, gradually replacing the reflux condensate supplied to the heating coil with a low boiling hydrocarbon oil distillate, highly heating the distillate in said heating coil and introducing the highly heated distillate into direct contact with the mass of coke in the chamber for the purpose of effecting its substantial devolatilization.

2. The method as defined in claim 1 further characterized in that said low boiling distillate contains a substantial quantity of hydrocarbons boiling Within the gasoline range and further in that this distillate is heated to reforming temperature in the coil.

3. The method as defined in claim 1 further characterized in that said low boiling distillate comprises gasoline-containing distillate separated from said evolved vapors by the fractionation of the latter, the distillate being heated to reforming temperature in the coil.

4. A conversion process which comprises heating heavy hydrocarbon oil to conversion temperature in a heating coil and subsequently distilling it to coke in an enlarged chamber, fractionating resultant vapors and then finally condensing the fractionated vapors, continuing the passage of the heavy oil through the coil and its distillation in the chamber until a substantial body of coke has accumulated in the latter, then discontinuing the supply of the heavy oil to the coil and passing a lighter oil, comprising reflux condensate formed by said fractionation, therethrough, heating the lighter oil in the coil to a temperature at least as high as that to which the heavy oil was heated in the coil, then introducing the lighter oil into contact with the body of coke in the chamber, then Iractionating the vapors of the lighter oil in contact with condensate formed by said final condensation Whereby to redistil this condensate, gradually replacing the reflux condensate supplied to the coil by liquid products of the last-named fractionation and heating these liquid products in the coil to cracking higher temperature, and introducing the thus heated liquid products into contact with the body of coke in the chamber.

5. In the coking of hydrocarbon oils wherein heavy hydrocarbon oil is heated in a coil and subsequently distilled to coke in an enlarged chamber and passage of the oil through the heating coil continued until a substantial body of coke has accumulated in the chamber, the evolved vapors fractionated and resultant reflux condensate returned to the coil for retreatment with the heavy oil; the method which comprises discontinuing the supply of the heavy oil to the coil when a substantial body of coke has accumulated in the chamber, continuing the return of reflux condensate to the heating coil, introducing the heated reflux condensate into direct contact with the mass of coke accumulated in the chamber, subsequently replacing the reflux condensate supplied to the heating coil with a lower boiling fluid and heating the latter in the coil to higher temperature than the reflux condensate, and

introducing the highly heated fluid into direct contact with the mass of coke in the chamber to effect substantial devolatilization of the coke.

LYMAN C. HUFF. 

